The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.
Reversible or erasable “magic” slates have been used as, for example, toys or educational tablets. Such slates include a plurality of layers of material which may, for example, be formed of plastic and/or paper. Pressure exerted on a top layer or cover of the slate, which is typically formed from a clear plastic film, results in a visible mark created from the temporary adhesion of a lower translucent (typically, cloudy or milky-colored) layer to, for example, a lower, colored (typically, black or dark gray) layer. The translucent layer releasably or nonpermanently adheres to the lower layer when pressure is applied to the top cover. This temporary adhesion results in intimate contact between the two layers allowing the transmittance of the color of the lower layer through the translucent layer and the top cover layer.
A number of slate systems enable erasing by physically lifting the top sheets to separate from the colored adhesive layer, by rubbing the surface which pushes captured air bubbles across and/or shifts upper layer resulting in separation of two layers, or by sliding a bar or other abutment member positioned between the wax-coated bottom black layer and the semi-transparent layer which separates these layers. All of these methods have drawbacks. Physical separating requires a multiple task motion of lifting one end of top film up and then replacing it so that it lies smoothly and squarely on the pad, thus requiring the use of two hands. The rub to erase method can only be used on smaller surfaces, requires multiple rubbings in many cases, and often fails to completely erase markings. Bar-types erasers add complexity, and have been reported to present difficulties in operating and erasing.
A magic slate erase system using an air pump to erase images pneumatically is disclosed in U.S. Pat. No. 3,943,643. The air pump is intended to erases images without requiring manual lifting of the top sheets to separate them from the wax-coated black layer, rubbing the surface, or pulling a bar. However, the air pump of U.S. Pat. No. 3,943,643, which is operatively connected to the cloudy/milky layer and the wax-coated black layer, does not efficiently remove air from the magic slate pad after the first erasing action. In inefficient removal of air makes it difficult for a user to draw subsequent next words/images because some air is left between the cloudy layer and the wax-coated layer. This residual air erases new writings/drawings immediately. Thus, the air left between the cloudy layer and the wax-coated layer requires users to wait for a long time before subsequent drawing action. Air remaining between the cloudy layer and the lower, colored, wax-coated layer makes the slate irreversible. There is a lack of consistency and reproducibility of the slate system in enabling marking while being able to easily and consistently erase such markings.